The present invention relates to an abnormal combustion detecting apparatus and method for detecting occurrence of abnormal combustion in an internal combustion engine, and also relates to a control apparatus and method using the abnormal combustion detecting apparatus and method for reducing vibration caused by abnormal combustion in the internal combustion engine.
In recent years, there is a tendency to employ mechanism of double over head camshafts in internal combustion engines to realize high-speed rotation and high output power. This type internal combustion engines are designed to exhibit high efficiency in operation at high speed. For example, the cam profile is designed so that the timing of opening/closing of intake and exhaust valves is designed to adapt to high-speed operation. Therefore, such abnormal combustion that the combustion pressure of some cylinder is reduced as compared with the pressure of normal combustion cylinder because of misfire, uneven combustion in cylinders, or the like, often occurs at the time of low-speed rotation such as at idling.
In general, a periodic torque fluctuation synchronous with the frequency of combustion strokes in each cylinder as shown in FIG. 2 (which shows the case where a four-cycle four-cylinder engine is used) is generated in a crankshaft of an internal combustion engine when the internal combustion engine is operated. The cyclic torque fluctuation causes torsional vibration in rotation shafts such as a crankshaft in the engine or in various kinds of apparatus driven by the engine. In an automobile engine, the reaction of the cyclic torque fluctuation may be transmitted from engine mounts to an automobile body to vibrate the body of automobile as a whole, so that vibration or inside noise may occur.
Assuming now that abnormal combustion as shown in FIG. 3 occurs in some cylinder, then output torque drops down remarkably in an instant compared with the output torque at the state of normal combustion. The reaction of the torque reduced by the abnormal combustion acts as vibration torque for vibrating the internal combustion engine itself and the automobile body in the same manner as the reaction of the cyclic torque fluctuation synchronous with the combustion frequency. Because the dropping (difference between the broken line and the solid line shown in FIG. 3) of torque caused by abnormal combustion occurs only in the cylinder of abnormal combustion, the envelope thereof is shaped like a single-shot pulse Accordingly, vibration torque as the reaction of the dropping of torque gives vibration to the engine and the automobile in the form of a single-shot pulse as shown in FIG. 4. At this time, a vibration having the combustion frequency generated in the engine and a vibration having the natural frequency of each of the internal combustion engine and the automobile are combined with each other in each of the engine and the automobile. Among these vibrations, the vibration having the natural frequency of each of the engine and the automobile is caused by single-shot pulse vibration torque as the reaction of the dropping of torque caused by abnormal combustion, so that the vibration exhibits the form of transitional vibration, so called, in which the vibration is attenuated with the passage of time.
In the case where an engine is set in a longitudinal direction with respect to an automobile as seen in an FR (front-engine rear-drive) car, that is, in the case where the axial direction of a crankshaft of an engine is equal to the direction of a roll axis of an automobile, the aforementioned reaction of the dropping of torque caused by abnormal combustion acts as vibration torque which brings the rolling of the engine and the rolling of the automobile. In general, the natural frequency of rolling in each of the engine body and the automobile is about 5 to about 10 Hz. At the time of low-speed rotation such as the time of the idling of the engine, however, the frequency in which abnormal combustion occurs is in the aforementioned natural frequency range of the rolling. If abnormal combustion occurs at the time of low-speed rotation, both the engine and the automobile are rolled so that an unpleasant feeling may be given to passengers. It is therefore necessary to reduce vibration of the engine and the automobile caused by abnormal combustion in the engine.
As one example of a technique for controlling vibration torque generated by the internal combustion engine, reference is made to Japanese Patent Unexamined Publication No. JP-A-61-171612 of Japanese Patent Application filed Jan. 28, 1985 by TOYOTA MOTOR CO., LTD. According to the disclosed technique, the torque fluctuation is reduced by generating reverse torque in the crank-shaft synchronously with the increasing of torque in the torque fluctuation generated with the frequency of combustion by the engine.
However, the aforementioned disclosed technique can cope only with the periodical torque fluctuation generated in the crankshaft synchronously with combustion in the engine. Accordingly, the disclosed technique cannot be applied to the vibration problem caused by the irregular torque fluctuation such as the torque dropping caused by abnormal combustion which occurs irregularly.
Further, in the aforementioned disclosed technique, the torque fluctuation generated by the engine is detected on the basis of the rolling acceleration of the engine detected by an acceleration pickup provided in the engine body. In the disclosed technique, such an acceleration pickup which is not provided originally in the engine must be provided newly.